What's the custard filling in a custard filled cake?

I have a request for a chocolate layer cake with custard filling for my neighbor's 1 year old birthday party, and I'm having a hard time with the custard filling part.

When someone asks for a custard filling, what is the custard filling?

So far I've made vanilla pastry cream (Herme), bavarian cream (Freiberg) and a vanilla cream filling (sugar, flour, salt, scalded milk, eggs, vanilla). Nothing's turning up quite right and I haven't had much luck on search engines or the major recipe sites.

Anyone know specifically what the filling is and able to share a recipe?

[Edit] Anyone know what to do with several quarts of the aforementioned fillings?

Kevin,i make the easyist filling ever ,ive done away with the whole pastry creams because thay dont freeze,This is also the filling i use fore vanilla slices,iset it in little disks then take the disks off freeze it on the tray,when frozen stack them in a box standing up,like little pellets,and then all i have to do is cook the puff pastry in disks and put together when ever the cake cabinets a bit empty.For your filling let it cool and use straight,or fould in some whipped cream,or better still some stiffed whipped imitation cream so it is airier
500mls water
500mls pure cream /45%butterfat
50gmscornflour or 3/4cornflour 1/4custard powder
50gms sugar /slug of vanilla
mix sugar and cornflour together with a bit of water
boil the cream and water ,pour it on the sugar mix,chesk sugar content ,its ready
We make this in 50 lt lots withthe sugar and cornflour in the big mixing bowl,mixing on low
when the 50 lts of cream/water boils,it must ba actually boiling up
[thats the secret fof large quantities]wheel it over to mixer ,turn off,pour in,turn on low ,it cooks the flours out in the bowl,sets perfectly .
goodluck gingernut